1. Field of the Invention
The invention relates to the field of propulsion systems and, in particular, to a propulsion mounting system for a non-ridged, semi-buoyant vehicle.
2. Description of Related Art
There are basically two main types of fully lighter-than-air vehicles; the rigid type or as it is more commonly called the "dirigible" and the non-rigid type or "blimp". Blimps basically comprise a single or multi-number of non-rigid gasbags wherein internal inflation pressure is used to form the external shape of the vehicle. A typical example of this design is found in U.S. Pat. No. 4,265,418 "Elongated Inflatable Structures For Flying Device Bodies" by M. Eymard the shape of the vehicle. The other basic type of lighter-than-air vehicle is the ridged design wherein an internal support structure is covered with a flexible material that serves as the outer skin. The vehicle may consist of a single gas chamber wherein the outer skin serves as the "gasbag" or can have numerous internal gasbags. An example of this concept can be found in U.S. Pat. No. 4,591,112 "Vectored Thrust Airship" by F. N. Piasecki, et al. However, both examples require that they be simultaneously loaded and unloaded in order to prevent the vehicle from "flying off." In fact, such vehicles must be tethered when on the ground during such operations. A particular limitation of the non-ridged design is that the flight station and cargo compartment generally must be mounted on the gondola at the bottom of the vehicle. The gondola is typically supported by catenary cables or curtains attached to the top of the gasbag. The dirigible design allows most if not all these components to be mounted within the main body of the vehicle, although most all incorporate a gondola of some sort. However, when the vehicle is extremely large there costs become prohibitive because the complexity of the internal structure. A problem with both designs is that, as fuel is consumed, the vehicle becomes lighter. In order to compensate for this increase in weight ballonnet systems are used. These typically comprise smaller inflatable compartments within the Helium filled bags that can be filled with air displacing "Helium volume", and reducing lift. Systems to reclaim water in the exhaust are also incorporated.
These two examples are true lighter-than-air vehicles in that the gas filled balloon generates all the lift. However, having the external contour of the vehicle in an aerodynamic lift producing shape can reduce the overall size of such vehicles and generally cost, for any given payload. Such vehicles not totally buoyant and take off in a manner similar to a conventional aircraft. In such designs, it is common practice to use a rigid internal frame (the dirigible concept) in order to maintain the proper contour. For example U.S. Pat. No. 3,486,719 "Airship" by J. R., Fitzpatick, Jr. While the Fitzpatick, Jr. design uses a rigid skin; most use a flexible gasbag with an internal frame structure. Of course there are non-rigid designs such as disclosed in U.S. Pat. No. 2,778,585 "Dynamic Lift Airship" by D. B. Tschudy. D. B. Tschudy's design includes a multi-lobe gasbag with a general aerodynamic shape, formed by catenary cables extending between the upper and lower surfaces of the vehicle.
However, there are problems with such vehicles, especially when they are very large. The generation of dynamic lift from the gasbag of the vehicle creates bending in the gasbag, which are much greater than found in conventional fully buoyant vehicles. Secondly, the lift-generating gasbag is much more aerodynamically unstable and therefore requires much larger tail surfaces than conventional, which in turn creates even greater loads on the gasbag of the vehicle. These two factors would tend to point toward the use of a rigid internal structure. It also allows great leeway in positioning the propulsion systems. However, it has been found designing a ridged internal structure that's light enough and simple enough to produce at a reasonable cost does not appear to be feasible at the present time. Thus a pressure-stabilized gasbag appears to provide the only viable solution. However, providing a gasbag design capable of absorbing flight loads, especially those induced by the vertical and horizontal stabilizers has proven difficult.
Prior art approaches such as disclosed by D. B. Tschudy uses a metal support structure at the rear of the gasbag absorb and distribute loads induced by the horizontal and vertical stabilizers into the gasbag. However, it is a complicated assembly. The three main lobes terminate in the same plane and support structure includes 3 connected cup shaped caps that attach to the ends of the three lobes. While such an approach provides some benefit, it would have insufficient effect in very large vehicle.
However, such placement does not allow for vectoring thrust. Mounting the propulsion system to the non-rigid air bag presents significant structural design problems. Thus most often they are mounted to the gondola in either a fixed position or on pylons so that thrust vectoring can be accomplished. An example can be found in U.S. Pat. No. 5,369,256 "Propulsion System For A Lighter-Than-Air Vehicle" by J. B. Kalisz et al. But this is not the optimum location for non-fully buoyant airships that are achieving a significant amount of aerodynamically produced lift.
Thus, it is a primary object of the invention to provide a propulsion system for non-rigid partially buoyant vehicle.
It is another primary object of the invention to provide a non-rigid partially buoyant vehicle having optimum positioned propulsion systems.
It is further object of the invention to provide a non-rigid partially buoyant vehicle having optimum positioned propulsion systems that are also easy to access for maintenance purposes.
It is a still further object of the invention to provide a non-rigid partially buoyant vehicle having optimum positioned propulsion systems that properly distributes thrust loads into the gasbag.
It is a still further object of the invention to provide a non-rigid partially buoyant vehicle having a propulsion systems that places engines in positions where the use of differential thrust will provide a means of directional control.